FIG. 1 shows partially a laser diode of the aforementioned type. This device 2 includes laser diodes 4 in the form of bars, schematically shown, and metal plates 6 between which the laser diodes are arranged. In order to power the laser diodes, plates 6 are electrically conductive. The electrical connection between plates 6 and laser diodes 4 is achieved in a manner known to those skilled in the art. In order to protect the laser diode itself, the latter can be associated with an electrically insulating bottom part of greater thickness than the material forming the laser diode. In the Figures annexed to the description of the present invention, the various elements or layers associated with a laser diode are represented schematically with the latter in the form of a bar 4.
The arrangement of plates 6 and the laser diodes thus allows an electrical current to pass along direction X. Some heat transmission is also obtained along this direction X via metal plates 6. In particular, plates 6 are made of copper. However, to allow efficient cooling, the heat generated by the diodes must be able to be evacuated by plates 6 in the direction of cooling body 10. This cooling body has, in a conventional manner, a conduit 12 for a water flow. Since the electrical current has to pass through the diodes along direction X, plates 6 must be electrically insulated from each other. In order to do this, in the prior art of FIG. 1, an electrically insulating ceramic layer 14 is welded to body 10 via a braze forming a film 16. Next, each plate 6 is welded to the layer 14 again using a braze 18. Plates 6 must be welded in a structured manner, to prevent any short-circuits between plates 6. One must therefore prevent the braze between a plate 6 and ceramic layer 14 being in contact with the braze used for welding another plate.
The device of the prior art described here has several drawbacks. First of all, making a structured weld for securing the plates to the insulating layer is a complex operation requiring particular precautions. Moreover, it is difficult to guarantee a good industrial yield for this operation given that braze 18 tends to stretch during welding. It will also be noted that a weld defines an interface that forms a brake on the heat transfer towards cooling body 10. In the case of FIG. 1, two layers of weld are present on either side of layer 14, which decreases the cooling efficiency of the laser diodes.
There is also known from US Patent No, 2004/0082112, a stack of laser diodes that differs from that shown in FIG. 1 essentially in that the insulating layer is structured. According to the teaching of this document, each plate is assembled in the bottom part thereof to an electrically insulating layer by a weld. This insulating layer is flat and has the same dimensions as those of the end of the plate. Each plate is thus first of all welded to its own insulating layer. Next, each assembly thereby formed is welded to the cooling body by means of a braze, affixed to the cooling body and structured so as to correspond to the distinct zones provided for the plurality of “plate-insulating layer” assemblies.
This latter embodiment of the prior art, just like that shown in FIG. 1, raises manufacturing problems. The structured weld defines a precise location for each plate on the cooling body. This raises a problem for machining the various elements, in particular a tolerances problem as to the plate thickness and the diode thickness. Indeed, variations in these thicknesses also cause an alignment problem of the diode and plate stack with the braze zones. Decreasing the tolerances in machining the plates and diodes increases the manufacturing cost. Moreover, the thickness of the diodes can vary substantially within the standard assortment of a laser diode manufacturer. It should also be noted that this thickness is not standardised such that it also varies from one supplier to another. A method such as that disclosed in US Patent No. 2004/0082112 thus raises a real assembly problem. Another problem arises from the fact that the height of the structured braze layer has to be low to remain substantially within the distinct zones provided. Thus, the plate height machining tolerance is also critical. If, during the prior assembly of the plate and laser diode stack, the bottom ends of the plates are arranged in the same geometrical plane to ensure that each plate will sit properly on the braze arranged in the corresponding zone on the cooling body when the plates are welded thereto, the laser diodes secured to the plates on the top end side thereof will not emit within the same emission plane, which raises a problem of collimation or focussing the laser beam generated by the plurality of diodes.
It is an object of the present invention to overcome the aforementioned problems by proposing a laser device with a stack of laser diodes that can be manufactured by a reliable industrial method the implementation of which is relatively easy. It is another object of the invention to propose a laser device of this type arranged so as to evacuate efficiently the heat generated by the laser diodes.